Field of the Invention
Embodiments presented in this disclosure generally relate to generating electrical power. More specifically, embodiments disclosed herein provide noise-shaped random pulse width modulation (PWM) for power converters.
Description of the Related Art
In variable speed generators, a frequency converter is used to convert power from the generator at a variable frequency to a predefined frequency corresponding to a load—e.g., a utility grid. In one example, the frequency converter converts the AC signal provided by the generator to a DC signal and then back to an AC signal with a frequency that matches the desired frequency of the load. To convert the DC signal to an AC signal with the desired frequency, the frequency converter may use pulse width modulation (PWM) based on a switching frequency.
Operating power converters with a constant switching frequency produces clusters of harmonic peaks in power output signals, which appear as spectral energy concentrated at several discrete frequencies. These harmonics generally produce “tonal” noise at various frequencies within the electromagnetic spectrum. Reducing or eliminating tonal noise may be beneficial, as some countries impose strict noise regulations that limit amounts of audible noise that may be generated by a generator. Additionally, tonal noise may result in electromagnetic interference (EMI) that degrades performance of the power converters. Random PWM (RPWM) has been developed to distribute concentrated spectral energy across a continuous noise spectrum, which attenuates the discrete harmonics and reduces the overall intensity of tonal noise.